[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Beta-lactams](https://durgical.com/en/pharmacology/classes/beta-lactams/) › Cefalexin [Pharmacology](https://durgical.com/en/pharmacology/) · [Beta-lactams](https://durgical.com/en/pharmacology/classes/beta-lactams/) # Cefalexin A first-generation oral cephalosporin for skin infections, pharyngitis, otitis and urinary infections due to staphylococci and streptococci. Updated 2026-11-01 - Class: [Beta-lactams](https://durgical.com/en/pharmacology/classes/beta-lactams/) - Enzyme: Penicillin-binding proteins (bacterial transpeptidases) - ATC code: J01DB01 - WHO Model List of Essential Medicines Also called: cephalexin ✂**Penicillin-binding proteins (bacterial transpeptidases)**Cefalexin ⓘ The figure shows cephalothin, a first-generation cephalosporin with the same core, acylating the Streptomyces R61 DD-peptidase, the classic PBP model; no structure of this drug bound to a PBP has been published. **Target in 3D:** Penicillin-binding proteins (bacterial transpeptidases). PDB structure 1CEG (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/1CEG) · Drag to rotate · pinch to zoom ## Mechanism of action Like every cephalosporin, cefalexin has a β-lactam ring fused to a dihydrothiazine ring. It acylates the PBPs and stops peptidoglycan cross-linking. It is first generation: very active against gram-positive cocci (streptococci and methicillin-susceptible Staphylococcus aureus) and some enteric bacteria such as E. coli, Proteus mirabilis and Klebsiella. It does not cover enterococci, MRSA or Pseudomonas. - Absorbed from the gut and reaches the tissues - Acylates the PBPs of staphylococci and streptococci - Wall cross-linking stops - The bacterium lyses ## Pharmacokinetics **Absorption** Good oral absorption. **Elimination** By glomerular filtration and tubular secretion; nearly all the dose leaves unchanged in the urine within a few hours. ## Indications - Skin and soft-tissue infections (cellulitis, impetigo) due to staphylococci or streptococci. [Cellulitis of the leg →](https://durgical.com/en/conditions/cellulitis-of-the-leg/) - Streptococcal pharyngitis and respiratory infections by susceptible strains. [Streptococcal pharyngitis →](https://durgical.com/en/conditions/streptococcal-pharyngitis/) - Otitis media. [Acute otitis media →](https://durgical.com/en/conditions/acute-otitis-media/) - Genitourinary infections by susceptible strains. [Urinary tract infection (acute cystitis) →](https://durgical.com/en/conditions/urinary-tract-infection/) - Bone infections due to S. aureus or P. mirabilis. [Osteomyelitis →](https://durgical.com/en/conditions/osteomyelitis/) ## Adverse effects ### Common - Diarrhoea, nausea, dyspepsia - Rash, hives - Genital itching and vaginitis ### Serious (rare, important) - Anaphylaxis - Clostridioides difficile diarrhoea, from mild to severe colitis - Positive direct Coombs test and, rarely, haemolytic anaemia - Seizures if it accumulates in kidney failure ## Contraindications - History of hypersensitivity to this or another cephalosporin; caution, and sometimes contraindication, after anaphylaxis to penicillins or other β-lactams ## Key interactions **Metformin** Cefalexin raises metformin concentrations; glucose and tolerance are monitored. **Probenecid** Reduces tubular secretion: higher and longer-lasting β-lactam levels. **Copper-reduction urine glucose tests** May give a false positive; enzymatic methods are used. ## What is monitored - Clinical response - Kidney function in older adults or with kidney failure ## Administration and safety - Oral, with or without food. - Do not confuse cefalexin with cefazolin or other cephalosporins with similar names. - Shake the reconstituted oral suspension before each use and store it as the pack says. ## Nursing care - Before the first dose: ask about allergy to penicillins, cephalosporins and other β-lactams, and what the reaction was. - After the first dose, watch for hives, wheeze, low blood pressure or swelling of lips and tongue, with anaphylaxis equipment at hand. - Teach the patient to report watery or bloody diarrhoea, even weeks after the course ends. - Stress completing the course even if the skin or throat improves. ## Pregnancy and breastfeeding Available data do not show a higher risk of birth defects; it is used in pregnancy when the infection requires it. ## Memory aid 'Cefa-LEX, law of the skin': first generation, oral, for skin gram-positive cocci. No first-generation cephalosporin touches enterococci, MRSA or Pseudomonas. ## Test yourself Think of the answer, then tap the question to see it. ## Which bacteria does no first-generation cephalosporin cover? Enterococci, methicillin-resistant Staphylococcus aureus (MRSA), Listeria and Pseudomonas aeruginosa. ## Which interaction with an oral antidiabetic does cefalexin's label describe? It raises metformin concentrations, through competition for renal secretion. ## How is cefalexin eliminated, and what does that mean in kidney failure? Almost all of it leaves unchanged in the urine; in kidney failure it accumulates and the risk of adverse effects, including seizures, rises. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/cefalexin/) ## Related drugs - [Cefazolin](https://durgical.com/en/pharmacology/cefazolin/) - [Dicloxacillin](https://durgical.com/en/pharmacology/dicloxacillin/) - [Amoxicillin](https://durgical.com/en/pharmacology/amoxicillin/) ## Related conditions - [Cellulitis of the leg](https://durgical.com/en/conditions/cellulitis-of-the-leg/) - [Streptococcal pharyngitis](https://durgical.com/en/conditions/streptococcal-pharyngitis/) - [Acute otitis media](https://durgical.com/en/conditions/acute-otitis-media/) - [Urinary tract infection (acute cystitis)](https://durgical.com/en/conditions/urinary-tract-infection/) - [Osteomyelitis](https://durgical.com/en/conditions/osteomyelitis/) [← Back to the class: Beta-lactams](https://durgical.com/en/pharmacology/classes/beta-lactams/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [Cephalexin: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682733.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [DailyMed - CEPHALEXIN capsule](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c0ca008e-0e28-412e-a58f-70f63817713b) (DailyMed (U.S. National Library of Medicine), 2026); [RCSB PDB - 1CEG: CEPHALOTHIN COMPLEXED WITH DD-PEPTIDASE](https://www.rcsb.org/structure/1CEG) (RCSB Protein Data Bank, 2026); Farmacología básica y clínica (Katzung), cap. 43 (McGraw Hill, 2025). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/cefalexin/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/cefalexin/